The Lunar Prospector line-of-sight acceleration data after terrain correction have been inverted to the high-resolution Bouguer gravity anomalies of the lunar nearside. Lithospheric thicknesses of the early Moon were investigated by comparing the gravity anomalies of craters and impact basins of various dimensions. The lithosphere was already thick enough to support craters with diameters up to 300 km in the Pre-Nectarian and Nectarian Periods. Degree of isostatic compensation of larger impact basins suggested lithospheric thickness of 20--60 km at that time, which depended more on localities rather than age differences.